Some vehicles are now equipped with anti-theft devices comprised of cellular telephone systems configured to transmit an emergency message when various sensors on the vehicle are triggered by events that usually accompany a collision or the vehicle's theft. These so-called stolen vehicle transmitter (SVT) devices are an effective theft deterrent because when provided with a global positioning system (GPS), they are also able to broadcast the location of the vehicle after it is stolen using location information obtained from the GPS.
Skillful car thieves are nevertheless able to steal a vehicle equipped with an SVT transmitter by jamming the control channel of a cellular telephone system with which the SVT is associated. While control channel jamming transmitters are unlawful, at least inside the United States, they can be purchased via the Internet. By jamming the control channel with a jamming transmitter, a vehicle's SVT is unable to request a frequency on which it can transmit an emergency message.
Techniques exist that can overcome control signal jamming but the use of those techniques can cause other problems if a spurious control channel signal is not from a car thief's jamming transmitter. Some businesses are known to employ control channel jammers in order to prevent customers from using cell phones on their premises. If a business maintains a cell phone control channel jammer, to prevent cell phones from being used, a vehicle anti-theft system that “hears” such a jamming signal will usually mistake such a jamming signal as a theft attempt and attempt to overcome the jamming signal. When a telematics service provider receives a signal from a SVT that indicates a vehicle is being stolen, the attention of law enforcement agencies will be needlessly diverted.